The present invention relates generally to communication networks, and more specifically, to shaper-scheduling methods and systems for implementing prioritized policing.
High speed networks are designed to carry services with a wide range of quality-of-service (QoS) requirements. Several datapath mechanisms have been proposed to satisfy various QoS requirements. One example is MLEF PHB (Multi-Level Expedited Forwarding Per Hop Behavior). The conceptual idea of MLEF PHB is to use a priority queue supplemented with a policer with various levels (thresholds) for different precedence levels. The different thresholds intend to facilitate dropping lower precedence packets before the higher precedence packets. One difficulty with MLEF is finding a suitable trade-off between sufficient threshold spacing across all levels to ensure appropriate differentiation across precedence levels (irrespective of packet arrival order) and short enough overall queue size to ensure sufficiently tight jitter bounds.
A conventional approach for prioritized policing is to utilize a policer to discard packets based on their precedence levels. The policer should not drop any packets when the traffic does not exceed the aggregate policing rate. When the traffic exceeds the aggregate policing rate, the policer should drop packets of lower priority levels to make room for packets of higher priority levels. Coupled policers (CP) may also be used. The coupled policers build upon the simple token bucket policer by allowing tokens to be shared among different token buckets. However, if multiple classes draw tokens from a common bucket, the resulting behavior depends on the arrival order and may introduce undesirable delays.
It is useful to define a hierarchy of traffic classes over which QoS requirements may be configured. A system which combines hierarchical shaping and scheduling with priority propagation is therefore desirable.